Spectroscope Info?

[beezaur]

I would like to see what my lights are throwing out for spectra, so I guess that requires a "spectroscope?"

The only thing I know about spectra=measuring instriments is a vague recollection of using a tabletop telescope-thing in physics lab.

I don't need anything fancy, but it would be nice to be able to get a rough number for spectral lines.

Would anyone be good enough to fill me in, or point me to some info?

Scott

 

[Tritium]

Try this link:
http://asd-www.larc.nasa.gov/edu_act/simple_spec.html

 

[beezaur]

Thanks, Tritium.

I found another link where you can use a CD or DVD instead of a diffraction grating: link

The link shows some good pics of flashlight spectra.

The thing I used in lab was a little bit like this:

I found some that might be handier to use that look like this:

Both are eBay items.

I don't really know what to look for in purchasing one. Edmund Scientific has one similar to the second pic that "measures" spectra, implying some sort of a scale that can be read. I remember from lab that we turned the telescope on the table, then did calculations from the angle reading to get the wavelength. I probably will build one, but I would like to buy a decent instrument too. Right now, I do not know what I am looking at, and I guess I need a bit of help with that.

Scott

PS: Thanks to ImageShack for Free Image Hosting

 

[Zelandeth]

Now that page on building your own looks handy. Going to give both methods there a try I think. Wanted a spectroscope for a long time, just never been able to come close to affording one!

 

[beezaur]

"just never been able to come close to affording one!"

For what it's worth, there are some on eBay for around $50 and less, the small cylindrical ones. I don't know if they are very useful though.

Scott

 

[The_LED_Museum]

I purchased one from Edmund Scientific for ~$25 last year.
You calibrate it by aiming it at a fluorescent light bulb and aligning a mark below the scale with the green mercury line in the fluorescent light with some type of external slider or something, and use it by looking through it and aiming it at the light source you want to view the spectrum of.

 

[Zelandeth]

Just finished building both those shown on the page. And they both work really rather well. The CD based one is probably the easiest to use thanks to the fact you don't have a blinding white line down the middle of the image (though you could block that out in the transmissive version with a bit of card or black tape in the middle of the viewing window). Shame my camera refuses to capture the spectra I'm seeing accurately.

 

[beezaur]

A little follow up here.

The itsy-bitsy spectroscope I ordered arrived today. It is a couple of inches long and about as thick as a fat pen. It doesn't really measure anything, but it does give a decent, if slightly out of focus, spectrum when you look at a light source. It satisfies my basic curiosity about what colors are given off by various light sources.

I can tell for certain now that my yellow-green Surefire A2 gives off a lot of red, green, and a bit of blue in addition to its dominantly yellow light.

I don't know if it was worth purchasing though. It is small and portable, but I doubt it outperforms the various do-it-yourself versions above.

Scott

 

[UVvis]

This thread has me interested.

I have a few UVvis detectors and flourescence toys in my labs. When I get some free time or have to do PM work on the instruments, I'll try scanning and see if I can get spectral and intensity information off of it.

 

[Zelandeth]

Okay, made a few photos of the spectra the transmissive hommeade one can produce - excuse the quality, my camera does NOT like low light situations.

Blue-green tinted 60W incandescent. Note, the camera also appears to be seeing two IR lines here as well, these appear from all the incan lamps. Appears that my camera has a "gap" for those wavelengths in the IR filter! Can clearly be seen where the filter on the bulb starts cutting out everything from the mid-red.

Next, a decent compact fluorescent. This one didn't come out so well. The actual image you see allows sufficient resolution to see precisely what's going on - however the camera overloads and the "blooming" wrecks that effect. The secondary spectra shows the resolution better - but is underexposed.

Now things get a little more interesting. Three coloured compact fluorescent lamps. Red, green and blue. To be honest, they're actually magenta, sage-green and bug-zapper blue. But have really interesting spectra as a result.

Firstly, the red one. Seems that the actual spectra here isn't that far off that of a normal fluorescent, just that there's far, far more red emission than you'd expect, and the violet line seems to have been attenuated somewhat, not a huge amount though. The phosphor itself glows a deep reddish pink when exposed to light from a BLB fixture. This reminds me of the magnesium fluorogermanate (I think) coating seen on high pressure mercury lamps.

Green one, now this *is* a bit of a puzzle, and I'm totally at a loss to explain the phosphor chemistry. The usual green line's there, very strongly too, but there's also pretty strong bands in the red, mid-blue and yellow. Hence the whitish green appearance. Anyone has a clue what the phosphor here is, feel free to tell me. Blacklight doesn't seem to cause any notable fluorescence from this one at all.

And the blue one. Just a conventional mercury spectra with a huge broadband blue emission stuck on the end. This one glows almost exactly the same colour as white paper when zapped with blacklight - not a million miles from the actual colour of the light. This is a lot dimmer than the other two.

Not great pics (though the blue one is actually pretty accurate (the seconday spectra - main one overloaded the camera). Think you can get the general idea when you extrapolate from the one overexposed and one underexposed one! Need to get a camera which has manual exposure control!

Hope this is of interest. One mod I made to the original plans was to paint the inside of the box matt black. This increased the contrast a lot as it got rid of all the reflections inside. Especially handy when dealing with bright sources.

 

[beezaur]

Zelandeth,

!

!!!

That is so cool!

Which spectroscope is that, the one using the diffraction grating? How does the CD/DVD version compare?

Pleased with your camera or not, those are great pics!

Scott

 

[Zelandeth]

Will get some photos of the unit itself shortly. I used the diffraction grating type (made both). Used the grating from a cheap pair of those glasses I got years ago. Just a cardboard box about 20cm long, narrow slit (I used a bit of CD for that too, as I didn't have anything else with a really, really flat edge laying around - and getting a CD to snap with a really flat edge isn't hard).

The most important points:

Get the edges of the slit as smooth and as level with each other as you can. Also, get them as close together as you can. The closer they are, the better the definition will be - but the dimmer the image will be. Trial an error is the key.

The diffraction grating MUST be so clean you could eat off it, otherwise you'll get huge amounts of blooming.

As I said earlier, painting the inside of the box helps contrast a LOT.

As for the CD one. It does work too, but not as well in my view. Firstly, the actual unit has to be a lot bigger. The first one could theoretically be made about an inch in diameter and as long as a pen. Whereas this has to be a pretty big box. It does, even with a CD produce a pretty well seperated spectra. The problem is though, that it tends to get cut off at one end or the other by the edge or hub of the CD. That and the image is much, much dimmer. Forget trying to get photos of this one without a decent camera. All I could get was a dim smudge. The spectra isn't as well defined as the first type either.

Works well enough if you haven't got an actual diffraction grating around, but the grating works better.